Method and apparatus for indicating the conditions in an absorbent article

ABSTRACT

A method and apparatus for gauging the levels of pH in the interiors of articles such as diapers, incontinence garments, pads, catamenial products, bedding, and would dressings are disclosed. This method and apparatus include sensing devices and relay systems for displaying the pH on the outside of the articles that provide visual and/or audible warnings that toxic levels are approaching and that it is time to remove and replace the article.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of application Ser.No. 08/949,965, filed Oct. 14, 1997.

FIELD OF THE INVENTION

[0002] The present invention relates to a novel method and apparatus formeasuring the pH in diapers and other such absorbent articles, and moreparticularly to a method and apparatus for signaling incipientpathogenicity in the environment of the article.

BACKGROUND OF THE INVENTION

[0003] With the increase of mothers employed away from home, and theincrease in adult diaper-wearers, there is strong demand for diapers andother disposable garments that can be worn for longer periods. To meetthis demand, superabsorbent and dry-feel materials have been developed.Most diaper products contain materials that can absorb many times theirweight in urine. They are normally worn for more than four hours andfrequently for eight hours or longer. Superabsorbent diapers thatfeature leakage barriers have also been developed, as well as newammonia odor control technologies.

[0004] Prior to these new technologies, it was commonly accepted thatthe human olfactory system was the ideal monitor for sensing the onsetof toxic ammonia concentrations. But the new diaper technologies havecaused such major changes in the pH levels and in the volumes,concentrations, and migration of ammonia gas in diapers, that olfactorysensing is no longer reliable. In addition, since new diapertechnologies channel urine away from the interior surface, leaving a dryfeel, the sense of touch can no longer inform the caregiver that thediaper may contain a substantial amount of urine.

[0005] Onset toxicity of anhydrous ammonia as a caustic agent occurs atconcentrations of 20 to 35 ppm. See NIOSH Criteria for RecommendedStandard Exposure to Ammonia #74-136; Proctor et al., Chemical Hazardsof the Workplace (2d ed. 1988). The human odor threshold for ammonia gasranges from 5 to 50 ppm, although regular exposure to low levels buildsolfactory tolerance for higher levels. In the new diapers, ammonia gasconcentrations can quickly reach 50 ppm, but the characteristic ammoniaodor is, to some degree, contained within the diaper barriers and/ormasked by new technologies designed specifically for that purpose. Thus,there is now a need for other methods to warn caregivers of ammoniabuild-up.

[0006] Within the diapered-area temperature and pH are higher thannormal, friction is greater and microbes multiply faster than innon-diapered areas. The skin is wetter than normal, non-diapered skin,and wet skin is more vulnerable to damage than dry skin. The combinationof these factors causes or contributes to diaper area pathologies.

[0007] Diaper-area temperature, microbiological load, and pH are greaterin disposables than in cloth diapers. The higher pH in disposablestriggers diaper dermatitis, the most prevalent of diaper area diseases.This disease is caused by the actions of proteolytic enzymes, whichmetabolize the skin and subcutaneous tissue.

[0008] Ammonia dermatitis, another diaper area disease, normally occursonly after healthy skin has been continuously exposed to ammonia atgreater than 10,000 ppm for more than 15 minutes. See Procter et al.,Chemical Hazards of the Workplace (2nd ed. 1988). In a diapered areawhere the epidermis has already been compromised, ammonia exacerbatesthe pre-existing condition.

[0009] Urine entering a diaper is sterile and has a pH of about 6.2.Ammonia gas escapes the urine. At this point, the entire diaper-area pHbegins to rise. It will continue to rise, at an increasing rate, untilthe diaper is changed or the urea exhausted.

[0010] Ammonia is small, polymorphous, and highly soluble in water, andis highly mobile. Ammonia is also soluble in lipids and can migrateacross many cell membranes. As the skin pH increases through the 7.0 to9.0 range, the alkalinity overcomes the lactic acid buffering capacityof the epidermis and inflicts caustic burning, causing ammoniadermatitis. In addition, ammonia gas is also a suffocant that can causelife-threatening stenosis or, if inspired suddenly, gastrointestinalreflex/reflux. Furthermore, ammonia is a sedative that, if inspiredgradually over time, can impair an infant's central nervous system andmedullary and adrenocortical functions.

[0011] A major concern regarding long-lasting, leak-proof diapers isthat the urine permeable membrane enclosing the absorbent matrix oftenleaks or ruptures, most often during the time period after urine pH hasreached about 8.5. During this period, free ammonia continuously buildsup within the diaper, and fluid pressures will continue to build withinthe absorbent core. The pressures of the fluids and gases against thediaper's liquid permeable topsheet matrix membrane are said to havereached the breakthrough point when an external mechanical pressure of0.5 psi forces fluids and gases to reverse-permeate the diaper's liquidpermeable topsheet and contact skin. Such mechanical pressures caninclude the wearer rolling over or the diaper being forcefully pressuredby unyielding objects, such as crib siding, a car seat or a wheelchair.When the pressures within the sheath increase past the breakthroughpoint, the topsheet may leak or rupture, releasing toxic dissolved andfree ammonia and carbon dioxide. The matter released may contain asignificant biomass inoculum of rapidly multiplying bacteria includingProteus supp. This highly toxic mix contacts skin, and, if present,feces and pre-existing lesions.

[0012] U.S. Pat. No. 4,231,370 to C. Mroz et al. relates to a disposablediaper having a wetness indicator that is a pH-change/color-changestripe visible from the exterior of the diaper. The indicator comprisesan absorbent color-change material (bromophenol blue) in a matrix ofhighly flexible latex adhesive. This indicator only indicates wetness;it does not measure or indicate pH changes or ammonia concentrations.

[0013] U.K. Patent No. 2 250 121 to Lee relates to a disposable diaperwherein moisture closes a circuit, activating an audible alarm signalingthat the diaper is wet.

[0014] French Patent No. 2 680 678 to Ly relates to the use of amoisture sensor linked to a transmitter in a diaper that sends a signalto a receiver kept by parents.

[0015] The prior art that notifies caregivers of wetness in a diaper hassome utility since wet skin is more vulnerable to damage than dry skin,but short-term wetness, in itself, is not damaging. Diaper-area wetnessbecomes dangerous to healthy skin only in conjunction with otherirritants. Prior art wetness indicators that rely on pH measurementfunction in a binary mode; that is, they indicate simply whether anarticle is wet or dry, with no indication of the degree of wetness. A pHindication based solely on the presence of urine is useful, but does notindicate whether the urine is decomposing and therefore shifting to amore alkaline pH, which will lead to an unsafe environment. While theprior art attempts to solve the urine-ammonia problem at its source,until now there has been no method for warning the caregiver that theharmful conditions are imminent.

SUMMARY OF THE INVENTION

[0016] The present invention provides a method and apparatus for warningthe caregiver of a diaper-wearer when the pH concentration within thediaper approaches a degree of toxicity that can cause or exacerbatedamage to the wearer's skin and other membranes.

[0017] With the foregoing and other objects, advantages and features ofthe invention that will become hereinafter apparent, the nature of theinvention may be more clearly understood by reference to the followingdetailed description of the invention, the appended claims and to theseveral views illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a graph illustrating the relationship of pH in thediaper to time from initial urination.

[0019]FIG. 2 is a perspective view, shown partially in cutaway, of theinterior of a diaper incorporating a chemically reactive indicatormeans.

[0020]FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2.

[0021]FIG. 4 is a perspective view of the exterior of a diaperincorporating a chemically reactive indicator means.

[0022]FIG. 5 is a perspective view of the interior of a diaperincorporating a chemically reactive indicator means.

[0023]FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5.

[0024]FIG. 7 is a perspective view of the interior of a diaperincorporating an electrochemical indicator means.

[0025]FIG. 8 is a perspective view of the interior of a diaperincorporating an electrochemical indicator means.

[0026]FIG. 9 is a diagram of a series of curves that may be used topredict pH kinetic variability in diapers.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Personal absorbent products become unsafe to the user whenharmful conditions develop in and around the absorbent article. Overtime, such harmful conditions can result in wearers' prolonged exposureto alkalinity and microbial toxins. The longer a diaper is worn, thefaster ammonia is formed and the faster pH rises. A fast-rising pHtriggers rapid proliferation of some microbes, such as urea positivebacteria and pathogenic gut bacteria which produce proteolytic enzymes.In a leak-resistant diaper, excrement may be added continually anddecomposes while the toxic by-products of decomposition have no means ofescaping the diaper's closed system.

[0028] The current invention addresses this problem by providingcaregivers a real-time indication of the alkalinity level in the diaper,as measured by the pH, and, subsequently, whether the diaper hasdeveloped harmful conditions or will do so imminently.

[0029] What is invented is a method and apparatus for predicting theremaining safe life of diapers and other absorbent articles (such asincontinence garments, wound dressings, catamenial products such assanitary napkins, dressings, and the like), and warning that the time tochange the absorbent article is imminent. The term “safe life,” as usedherein, means the period of time during which the absorbent article doesno harm to the wearer.

[0030] In one embodiment of the present invention, a chemically reactivemeans is incorporated into the diaper that will provide ongoing visualindication of the pH of the environment in and around the diaper. Bycontinuous measurement and indication of the pH at various sites in thediaper, the presently claimed invention predicts the failure of thediaper at those sites. Since conditions at each location worsencontinuously over time, it is not possible to make useful predictions onthe basis of a single observation. Therefore, this must be akinetics-based measurement.

[0031] Urine enters a diaper at a normal pH of about 6.2, ranging up toabout 7.2, depending on the pathological condition of the wearer. Theurine-urea undergoes deamination by urease-producing bacteria. Withurease as the catalyst, ammonia begins to be formed in the urineaccording to the formula CO(NH₂)₂+H₂O→CO₂+2 NH₃. Ammonia is continuouslyformed, and the pH of the environment rises. At about pH 7.5 to 8.5 thefollowing reaction commences: CO(NH₂)₂+2H₂O→HCO₃ ⁻+NH₄ ⁺NH₃. The factorsthat determine the rate of ammonia production and pH rise includetemperature, available urea, the biomass of the inoculum ofurea-positive organisms present, the wetness and pH of the skin, thevolume of urine, and the mass, moisture content and bacteria content ofthe feces. Long-lasting diapers first begin to be toxic when the urinepH reaches about 6.5 to 7. Generally, this level is reached betweenabout 4 and about 5 hours after the wearer urinates, although it may bereached as early as hour 2.5 or as late as hour 9.

[0032] The second major period of toxicity occurs when the urine pH isbetween about 7.5 to 8.5. Generally, this period begins about 5 hoursafter the wearer urinates, although it may begin as early as about 3hours or as late as about 10 hours after urination. At this pH level,ammonia gas begins to enter the diaper's absorbent core.

[0033] The third major period of toxicity begins when the urine pHreaches about 8.5. Generally, pH 8.5 is reached at about 5.5 hours afterthe initial urination, although it may begin as early as about 3.25hours or as late as about 11 hours after the initial urination. Duringthis period, the concentration of ammonia gas will begin to permeateback through the membrane topsheet around the absorbent core. Therapidly rising pH increases the activity of many proteolytic enzymes;the free ammonia contacts skin and, if any, feces. Ammonium hydroxideforms and may reach concentrations as high as 1.5%. Caustic irritationand burning of skin and other membranes will continue with increasingseverity until the diaper is removed.

[0034] Because of the many factors determining the rate at which adiaper becomes unsafe to the wearer, the useful life span of a diapercan vary greatly, as shown in FIG. 1. Thus, it is not possible to setforth a precise schedule at which each stage of toxicity will be reachedand how much time remains before a diaper must be changed to avoiddamage to the wearer and/or the leak or rupture of the diaper. In orderto provide caregivers information they can use to make a timely change,it is very useful to keep them informed about the ongoing shifts in pHto increasingly alkaline values leading up to unsafe conditions. In apreferred embodiment, there will be one or more pH indicators thatchange color during each of the periods of toxicity described aboveincorporated into the diaper and visible to the caregiver.

[0035] Such a series of indications is useful in maintaining healthyskin for all users, and particularly when the wearer is sensitive tosmall shifts in alkalinity, such as when the wearer has a pre-existingcondition where stratum corneum is compromised. The remaining timebefore the diaper becomes unsafe depends in part on the condition of theskin of the wearer. To prevent exacerbation of pre-existing skin damage,wearers with compromised skin should have a diaper change as soon aspossible after an indication that the pH has reached the first toxicitylevel (preferably within 30 minutes) and before the appearance of thesecond indicator color change indicates that the second major period oftoxicity has been reached. Wearers with healthy skin should have adiaper change as soon as possible after the second indicator colorchange to prevent skin irritation. If the third stage of toxicity isreached, the diaper must be changed immediately. If the diaper is notchanged until an indication that the third toxic stage has been reached,severe skin irritation and leaks or ruptures of the diaper are likely tooccur.

[0036] Attendants can readily learn from experience how to “read” thecolor change indicators with a sense of timing for the color changesthat will occur if the diaper is not changed. That is, attendants caninterpret the color change timing to know that the diaper will becomeunsafe in a predictable period of time. The time sequence for theammonia formation and pH rise in superabsorbent, leak-proofed diapersincludes so many variables that the timing and stages for the indicatorsignals must be fairly broad-ranged; however, precise timing is notrequired since the indicator signals are predictive, not simplyrecordations.

[0037] Referring now in detail to the drawings herein, like parts beingdesignated by like reference numerals throughout, there is illustratedin FIG. 2, a perspective view of a diaper that is designated generallyby reference number 10.

[0038]FIG. 2 illustrates a liquid-permeable topsheet 11 in facingsuperimposed relation with the inner surface of a liquid-impermeablecoversheet 12, and an absorbent core 13, which is located betweentopsheet 11 and coversheet 12. When placed on the wearer, it is thetopsheet side that will be in contact with the wearer's skin. A receptor14 is located between topsheet 11 and absorbent core 13. The receptor iscontacted by urine, which is then transported to a chemically reactivemeans (not shown). The chemically reactive means will involve a sensorthat responds to a change in pH and indicates this response visually bya color change. Thus, the chemically reactive means can be considered acombination sensor-indicator. Alternatively, there may be multiplereceptors in place of the receptor 14. The placement of receptors mayvary from one type or size of diaper to another.

[0039] The absorbent core should be capable of absorbing or retainingurine and other body exudates. The absorbent core is preferablycompressible, conformable, and non-irritating to the skin. It mayinclude any of a wide variety of liquid-absorbent materials commonlyused in absorbent articles, including comminuted wood pulp, meltblownpolymers including coform, chemically stiffened, modified orcross-linked cellulosic fibers, synthetic fibers such as crimpedpolyester fibers, tissue including tissue wraps and tissue laminates,absorbent foams, absorbent sponges, superabsorbent polymers, absorbentgelling materials, or any equivalent material, or any combination ormixture of these materials.

[0040]FIG. 3, a cross-sectional view of the diaper of FIG. 2,illustrates the receptor 14 located between topsheet 11 and absorbentcore 13, a conductor 15 located between receptor 14, and asensor-indicator 16 located between the absorbent core 13 and thecoversheet 12. The receptor 14 is contacted by urine, which is taken bythe conductor 15 to the sensor-indicator 16, which is visible throughthe coversheet 12. The coversheet 12 may be transparent or may contain atransparent section 17, through which the sensor-indicator 16 is visibleto the caregiver.

[0041]FIG. 4, a perspective view of the exterior of the diaper of FIG.2, illustrates the sensor-indicator 16, which is visible through thetopsheet 12, if transparent, or through a transparent section thereof.

[0042] One or more receptors, as shown in FIG. 2, provide measurementsfrom various locations because the flow of urine and gases in and aroundthe diaper causes variations in pH at different zones in and around thearticle. Urine enters the diaper, passes through the topsheet, and iswicked and channeled through the absorbent core for storage at thefarthest remove from the location where feces tend to collect.Receptors, such as fibrous materials and other wicking agents well knownto those skilled in the art, are placed in the absorbent core totransport urine to the sensor-indicator.

[0043] The receptors shown in FIGS. 2 and 3 are contacted by urine andpass the urine along a conductor 15 as shown in FIG. 3. The conductormay be a fibrous strip or any porous material that can conduct theurine. The urine is conducted along 15 to a sensor-indicator 16, locatedon the interior of the coversheet 12, as shown in FIG. 4, which isvisible to users and caregivers.

[0044]FIG. 5 illustrates a perspective view of another diaper thatincludes the sensor-indicator system of the present invention,designated generally by reference number 20. There is a liquid-permeabletopsheet 21 in facing superimposed relation with the inner surface of aliquid-impermeable coversheet 22, and an absorbent core 23, which islocated between topsheet 21 and coversheet 22. An insertion channel 28is formed as a pocket between the coversheet 22 and the topsheet 21 thatallows for insertion of a stick 29 adjacent to absorbent core 23. On thestick 29 there is a sensor-indicator 26. The stick 29 is inserted intothe insertion channel 28 such that the sensor-indicator 26 contacts theurine in the absorbent core 23. Alternatively there may be multiplesensor-indicators 26 on the stick 29 or elsewhere on the diaper. In oneembodiment, the stick 29 may be removed so that the color change onsensor-indicator 26 may be viewed; alternatively the coversheet 22 overall or a portion of insertion channel 28 may be transparent so thatcolor changes on the sensor-indicator 26 may be viewed without removingthe stick 29.

[0045]FIG. 6, a cross-sectional view of the diaper of FIG. 5,illustrates the insertion channel 28 located between topsheet 21 andabsorbent core 23. The insertion channel 28 contains the stick 29, whichis adjacent to absorbent core 23, so that the pH changes of the urine inabsorbent core 23 can be detected and visibly indicated by thesensor-indicator(s) (not shown in this view) on the stick 29.

[0046] Urine is discharged into the diaper at up to 15-20 ml/second, butis only taken up by the absorbent core at a rate of about 8 ml/second.The urine that is not immediately taken up puddles against the skin andcontacts feces, if any, before it is absorbed. As previously noted, thepH of this urine rises faster than urine at any other location in thediaper, because feces contain urea-cleaving bacteria that speeddeamination.

[0047] Initially, the take-up rate of the absorbent core increases onceit is wetted. Subsequently, as the absorbent core becomes increasinglysaturated, the take-up rate slows and the volume of urine puddlingagainst the skin and feces increases. The urine that puddles against theskin and feces contacts the area of the diaper that form leg openings.Accordingly, for greater accuracy in predicting the remaining safe lifeof the diaper, additional receptors may also be placed in this area.

[0048] The sensor-indicator is coated and/or impregnated with chemicalsfrom the group that respond to pH changes in the range. When the urinecontacts the sensor-indicator, chemical reactions are initiated whichresult in series of color changes indicative of the urine pH. Many colorchange pH indicators are commercially available for the pH range of 6.0to 10+.

[0049] A preferred sensor-indicator contains an indicator that changescolor at in the pH range between about 6.5 and about 7.5, preferablybetween about 6.6 to about 7.3, and then changes color again at a pH ofabout 7.5 to about 10 or more. Preferably there is a third indicatorcolor change at a pH between about 8.5 and about 10, preferably betweenabout 8.5 and about 9.0. This may be achieved by using a mixture ofseveral different dyes, selected such that the mixture provides distinctcolor changes at the required resolution (e.g., every 0.5 pH unit). Asimple example of such a mixture is one containing phenol red and thymolblue. With such a mixture, a progressive increase in pH from below 6.6to over 9.6 might be indicated by color changes from yellow to orange topurple.

[0050] Alternatively, multiple indicators, each changing color over adifferent pH range may be used. For example, a strip containing a seriesof small, discrete indicators that change color, separated by buffersand hydrophobic dividers, may be used. Such strips are commerciallyavailable, such as BAKER-pHIX® narrows range Universal pH IndicatorSticks. These indicators contain four distinct stages that change colorover ranges 6.0-7.7 and 7.5-9.5

[0051] Other means of visibly indicating pH means may be used, such asalpha numerics, i.e. “A, B, C, ” or graphics, i.e. a green to yellow tored array of indicators like a traffic light or a bullseye.

[0052] Color change indicator materials for ammonia and pH are wellknown and widely commercially available. They are commonly manufacturedas film coatings or emulsions comprising various cellulosic and/orpolymeric components including gels, adhesives and other materials in amatrix. Ammonia indicators, such as azoic dyes that react with ammoniaand cause a color-change, are commercially available from TennesseeEastman Company and others. Azoic dyes can be buffered and combined withother dyes to provide a broad spectrum of hues of varying intensities.

[0053] The following table lists commercially available pH indicatormaterials that are specific to the stages of pH levels described herein.pH Range pH Indicators Color Change 6.2-7.6 Bromothymol blue yellow toblue 6.4-8.0 Phenol red yellow to red 6.6-8.6 m-Nitrophenol colorless toyellow 6.8-8.0 Neutral Red bluish-red to orange-yellow 7.0-8.0 Quinolineblue colorless to violet 7.2-8.8 Cresol red yellow to red 7.3-8.71-Naphtholphthalein colorless to blue-green 7.6-9.0 Metacresol purpleyellow to purple 8.0-9.6 Thymol blue yellow to blue 8.0-9.6 p-Xylenolblue yellow to blue 8.2-9.8 Phenolphthalein colorless to purple 8.2-9.8o-Cresolphthalein colorless to red/violet  9.3-10.5 Thymolphthaleincolorless to blue 10.0-12.1 Alizarin yellow GG colorless to yellow10.1-11.1 Nile blue blue to red  9.8-11.0 α-Naphtholbenzein yellow toblue 10.2-12.0 Alizarin Yellow yellow to red

[0054] One of skill in the art can select appropriate indicators fromthe list (or any other commercially available indicators) suitable foruse in the present invention.

[0055] The dyes can be immobilized on an absorbent material such aspaper, or to a small absorbent pad or fibrous strips. The paper can beplaced in the diaper in such a way that it comes in contact with urineand is visible outside the diaper. Various treated papers and tapes thatchange color in the above pH ranges can be bonded to the diaper interiorand extended to the outer surface; such materials include universal andintermediate indicators sold by Hydrion Papers, EM Corp., and others.

[0056] The paper, pad or strip may be fixed to the inner surface ofcover sheet 12 at manufacture and viewed through transparent window 16.Alternatively, the pad may be attached to a removable plastic strip andviewed by withdrawing the strip periodically, or the dyes may be applieddirectly to the absorbent article or to a small absorbent pad or fibrousstrip that can be inserted in the diaper at a suitable location.

[0057] In another embodiment of the present invention, the pH indicatingmeans may be an electrochemical indicator.

[0058]FIG. 7 illustrates a diaper 30 having an electrochemical indicatormeans in accordance with one embodiment of the present invention. Diaper30 also includes an absorbent core 32, which is provided sandwichedbetween a liquid-permeable topsheet 33 and a liquid-impermeablecoversheet 39. Electrochemical indicator 32 may be inserted into diaper30 through an insertion channel 31. Insertion channel 31 is locatedprimarily between absorbent core 32 and topsheet 33.

[0059] Electrochemical indicator 32 includes an electrochemical cell 35coupled to a terminator 36 by a number of conductive lines 37.Electrochemical cell 35 is preferably a combination of a pH sensor and areference electrode. The pH sensor preferably provides an electricalsignal that contains information about conditions within diaper 30, suchas an electric potential that depends on pH. Electrochemical cell 35should preferably be able to reside in an absorbent article without itsperformance being compromised.

[0060] Suitable sensors for electrochemical indicator 32 include glassor polymer membrane electrodes, metal-metal oxide electrodes, metaloxide electrodes, and ion-sensitive field effect transistors (ISFETs).Suitable metal-metal oxide electrodes include antimony/antimony oxide,aluminum/aluminum oxide, and iridium/iridium oxide. Iridium-iridiumoxide electrodes, for example, are insensitive to most ions such ascopper, sodium, and potassium, and are not affected by oxygen, carbondioxide, ammonia, and hydrogen sulfide. They can be stored dry over along period. Suitable metal oxide electrodes include, but are notlimited to, iridium oxide and osmium oxide.

[0061] Combination glass membrane electrodes are commercially available.These combination electrodes contain an internal reference electrodetogether with the pH sensor. Rugged reference electrodes containingsilver/silver chloride and copper/copper sulfate couples arecommercially available.

[0062] Solid state reference electrodes have been described in thetechnical literature. A suitable electrochemical sensor for use inabsorbent products, such as diapers, might be comprised of a metal-metaloxide pH electrode and a solid state reference electrode.

[0063] An electrochemical potential from the pH sensor is measured withrespect to the potential of the reference electrode. The potentialdifference may be displayed on a simple meter 38 which is coupled toterminator 36. Meter 38 is preferably configured to indicate the pHwithin diaper 30 and provide information as to when diaper 30 should bechanged. In a preferred embodiment, meter 38 is portable and preferablysmall enough to clip on to the outside of the absorbent article.

[0064]FIG. 8 illustrates another diaper, designated generally byreference number 40, having an electrochemical indicator means inaccordance with one embodiment of the present invention. Diaper 40 issimilar to diaper 30 referred to in FIG. 7, however the electrochemicalindicator is designed not to be removed from diaper 40. Diaper 40 alsoincludes an absorbent core 42, which is provided sandwiched between aliquid-permeable topsheet 43 and a liquid-impermeable coversheet 44.

[0065] The electrochemical indicator of FIG. 8 includes anelectrochemical cell 41 coupled to a terminator 45 by a number ofconductive lines 46. Electrochemical cell 41 is preferably a combinationof a pH sensor and a reference electrode operating in the same fashionas electrochemical cell 35 of FIG. 7. Electrochemical cell 41 ispreferably located between absorbent core 42 and topsheet 43. Terminator45 is preferably located on the periphery of diaper 40 so that it may becoupled to a pathogenic prediction meter 47.

[0066] Pathogenic prediction unit 47 is a more sophisticated version ofmeter 38 of FIG. 7. Pathogenic prediction unit 47 incorporates ananalog-to-digital converter, memory (dynamic random access memory, orDRAM), and a microprocessor. The voltage signal from the sensor may thusbe recorded by converting it into a digital form, which is stored in thememory. The stored voltage data represents the pH as a function of time.The pH-time dependence may be displayed visually by pathogenicprediction unit 47 or electronically analyzed by the microprocessorusing a curve-fitting procedure as described below.

[0067]FIG. 9 is a diagram of a series of curves 51, 52, and 53 that maybe used to predict to pH kinetic variability in diapers in accordancewith one embodiment of the present invention. Although more curves maybe used, for ease of illustration, only three curves are shown. Eachcurve represents a pH-time equation that may be used to predict how longit might take to reach a preselected pH value. As the pH sensor monitorspH levels in a diaper at regular intervals, it will generate a series ofdata points 54 that are compared to curves that are stored in memory,such as curves 51, 52, and 53. As soon as the best curve fit isidentified, which in this example is curve 55, the microprocessor willlocate the point on that curve where pH reaches a dangerous level. Thedangerous pH level in this case is indicated by point 55 at a pH of 7.5.

[0068] The dangerous pH level may be adjusted according to the skincondition of the diaper wearer. The microprocessor may then compute thelength of time it should take to reach a dangerous pH level based on thecurve. Because the process of measuring pH and curve matching continuesthroughout the time in which the diaper is worn, different curves may beselected adjusting to the new data points. However, changes in theprojected time it should take to reach a dangerous pH would be buffered,so as to gradually change, and not be overly responsive to statisticallyinconsistent changes. The length of time may be displayed on apathogenic prediction unit 55 along with the current pH of the diaper.

[0069] In another preferred embodiment of the present invention, therelays and signals of the pH sensor are calibrated to provide warningsignals that the pH levels and gas concentrations in the diaper willbecome pathogenic at a predicted time, preferably 10 to 30 minutesbeforehand. The electric signal generated by the sensor may result in avisual indicator, which changes color based on the pH. The color changesignals should be clear, well-paced, and easily visible on the diaperexterior. The electric signal generated by the sensor may also result inan audible signal that is loud enough to warn the wearer or a caregiverthat the diaper must be changed.

[0070] By providing these signals, this improved diaper permitscaregivers to be more efficient, and provides wearers with greatercomfort and safety. Used properly, a diaper in accordance with thepresent invention provides protection against dermatological conditionscaused by extended exposure to alkaline environments, and more rapidhealing of pre-existing dermatological conditions. Thus, the inventionis believed to provide urgently needed utilitarian benefits, as well asuseful social benefits.

[0071] While this invention has been described with respect to anabsorbent article in the form of a disposable or reusable diaper, itwill be appreciated that the invention could be applied to otherabsorbent products such as but not limited to, diaper insert pads,feminine hygiene products, incontinence products, bedding, bandages, andother such articles.

[0072] Although certain presently preferred embodiments of the inventionhave been described herein, it will be apparent to those skilled in theart to which the invention pertains that variations and modifications ofthe described embodiment may be made without departing from the spiritand scope of the invention. Accordingly, it is intended that theinvention be limited only to the extent required by the appended claimsand the applicable rules of law.

What is claimed is:
 1. A method for determining the remaining safe lifeof a diaper comprising the steps of: applying a diaper to a subject,said diaper having means for indicating by a visual color change the pHof the interior conditions of said diaper; observing the color of theindicating means; determining from the color of the indicating meanswhether the pH has reached a level at which the safe life of the diaperhas ended.
 2. A diaper comprising: a liquid impervious outer layerhaving opposed side edges and opposed end edges connecting the sideedges, said outer layer defining the shape and dimensions of the diaper,the diaper having a crotch portion adapted to engage the crotch of thewearer to capture and retain body waste material when the diaper isfolded medially and worn engaging the waist and stomach areas; anabsorbent second layer adapted for receiving body waste material, theabsorbent pad having opposed side and end edges, the absorbent pad beingslightly narrower than said first layer, the side edges of the firstlayer extending around and over the side edges of the second layer,thereby providing a barrier against body waste material from escapingthrough the back of the diaper or through the side edges of the pad; ameans for measuring pH, located within said absorbent second layer, saidmeans being capable of indicating multiple changes in the pH of theinterior environment of the diaper; and a means for conveying saidindication of multiple changes to the exterior of the diaper.
 3. Thediaper of claim 2, wherein multiple changes in pH are indicated by avisual color change.
 4. The diaper of claim 1, wherein the means capableof indicating multiple changes in pH indicates said changes audibly. 5.A method for monitoring changing conditions in a diaper comprising thesteps of: applying the diaper of claim 3 to a subject; and observingsaid color change over time.
 6. A method for determining the remainingsafe life of a diaper, comprising the steps of: applying the diaper ofclaim 3 to a subject; observing said color change over time; anddetermining from the rate of change of said visual indicator the amountof time remaining in the safe life of the diaper.
 7. A diapercomprising: an electrochemical indicator for measuring pH of an interiorenvironment of said diaper, said electrochemical indicator being locatedwithin an absorbent core layer of said diaper, wherein saidelectrochemical indicator is operable to measure a series of pH levelsover time and generate a series of electrical signals based on saidseries of pH levels; a pathogenic prediction unit operable to receivesaid series of electric signals, wherein said pathogenic prediction unitperforms curve matching on said series of pH levels and determines atime at which said interior environment of said diaper is predicted tobecome pathogenic based on a selected curve.
 8. A diaper as recited inclaim 7, wherein the electrochemical indicator includes anelectrochemical cell having a pH sensor and a reference electrode.
 9. Adiaper as recited in claim 8, wherein the electrochemical indicatorfurther includes a terminator coupled to the electrochemical cell by anumber of conductive lines, wherein said terminator is coupled to thepathogenic prediction unit.
 10. A diaper as recited in claim 9, whereinsaid pathogenic prediction unit displays a current pH of the interiorenvironment of the diaper.
 11. A diaper as recited in claim 10, whereinsaid pathogenic prediction unit displays the time at which the interiorenvironment of the diaper is predicted to become pathogenic.
 12. Adiaper as recited in claim 10, wherein said pathogenic prediction unitdisplays an amount of time remaining until the interior environment ofthe diaper is predicted to become pathogenic.
 13. A method of predictingthe remaining safe life of a diaper, comprising the steps of: measuringa series of pH levels of an interior environment of said diaper;matching a selected curve to said series of pH levels by comparing saidseries of pH levels with a series of curves; and predicting a time atwhich said interior environment of said diaper will have a pathogenic pHbased on said selected curve.
 14. A method of predicting the remainingsafe life of a diaper as recited in claim 13, further comprising thestep of indicating a time remaining until the predicted time at whichthe interior environment of the diaper will have a pathogenic pH.
 15. Amethod of predicting the remaining safe life of a diaper as recited inclaim 13, further comprising indicating a time at which the diapershould be changed based on the predicted time at which the interior ofenvironment of the diaper will have a pathogenic pH.
 16. A method ofpredicting the remaining safe life of a diaper as recited in claim 15,wherein said indicating a time at which the diaper should be changedincludes a visual indicator.
 17. A method of predicting the remainingsafe life of a diaper as recited in claim 16, wherein said visualindicator includes a color change.
 18. A method of predicting theremaining safe life of a diaper as recited in claim 15, wherein theindicating a time at which a diaper should be changed includes anaudible signal.